1. Field of the Invention
The present invention relates to a multistage oil seal for a motor used in a machine tool and to a machine tool motor using the oil seal.
2. Description of the Related Art
An oil seal of rubber or the like is generally used in the shaft seal part of various machines in order to prevent the leakage of the sealed fluid or the intrusion of foreign matter such as a liquid, or the like, from the outside.
In a machine tool, a workpiece is machined with a tool while a cutting fluid is ejected to the machined area to cool it. Accordingly, the cutting fluid is liable to fly in all directions and intrude into the inside of the machine tool. To prevent this inconvenience, an oil seal is disposed around the rotary shaft or the like to keep the cutting fluid out of the internal mechanism of the machine tool.
As an example of such an oil seal, a rotational oil seal is known, as described as a prior art in Japanese Unexamined Patent Publication No. 2002-139156, in which a plurality lips in a plurality of stages for closely contacting with a peripheral surface of a rotary shaft are disposed along an axis of the rotary shaft in a sealing portion formed along the peripheral surface of the rotary shaft to secure pressure resistance for an improved seal effect.
In recent years, on the other hand, various cutting fluids have been developed to improve the machining efficiency of the machine tool, and each machine tool user conducts the machining using the most suitable cutting fluid among them. Therefore, depending on the components of the cutting fluid used, a chemical change or a swelling can occur in the oil seal lip, thereby resulting in a reduced seal function or a sealing failure.
The cutting fluid for use with a machine tool can be selected as desired by the user of the machine tool, and therefore cannot be predicted by the machine tool manufacturer. This poses a problem that it is difficult to make a lip, used for an oil seal to prevent the intrusion of a cutting fluid, from a material suitable for preventing the deterioration of the seal function due to the chemical change or the swelling, for all possible cutting fluids.